.wrap of a method breaks callsame/nextsame/etc.

[vrurg]

The Problem

Wrapping a method in a child class breaks MRO chaining for callsame/nextsame. Consider the following code:

     class Foo {
         has Int $.attr is rw;

         method m {
             say "<this is Foo:m>";
             callsame;
         }
     }

     class Bar is Foo {
         method m {
             say "<this is Bar::m>";
             callsame;
         }
     }

     class Baz is Bar {
         method m {
             say "<this is Baz::m>";
             callsame;
         }
     }

     Baz.^lookup( 'm' ).wrap( method { say "<this is WRAPPER:m>"; nextsame } );

     my $inst = Baz.new;

     $inst.m;

It produces the following output:

<this is WRAPPER:m>
<this is Baz::m>

Method m of class Baz cannot call the next method in MRO chain.

There is even worse case scenario if wrap is applied to Bar::m method. Replacing the wrapping line in the source with the following:

Bar.^lookup( 'm' ).wrap( method { say "<this is WRAPPER:m>"; nextsame } );

gives us:

<this is Baz::m>
Cannot invoke object with invocation handler in this context

Environment

• Operating system: macOS 10.13
• Compiler version (perl6 -v): This is Rakudo version 2018.06 built on MoarVM version 2018.06

[vrurg]

There is interesting development for the situation when the method in Bar is wrapped. Adding a call to nextcallee into Baz::m:

     class Baz is Bar {
         method m {
             say "<this is Baz::m>";
             my &nc = nextcallee;
             #self.&nc;
             callsame;
         }
     }

avoid the exception about invocation handler. Instead the following output is produced:

<this is Baz::m>
<this is Foo:m>

It looks like this time callsame just got around Bar::m by simply ignoring it! By uncommenting the self.&nc call I get the expected output:

<this is Baz::m>
<this is WRAPPER:m>
<this is Bar::m>
<this is Foo:m>

but the point that it is produced by two separate calls. I.e., callsame from Bar::m did not pass the control to Foo, but from Baz::m did!

Now, the final trick: leave the self.&nc but comment out callsame in Baz::m. It raises another exception:

<this is Baz::m>
Cannot invoke this object (REPR: Uninstantiable; Callable)
  in method m at ./wrap.p6 line 23
  in block <unit> at ./wrap.p6 line 32

These tests were made with a recent rakudo checkout: This is Rakudo version 2018.06-407-g3301ddb1c built on MoarVM version 2018.06-399-g4fc267b60

[vrurg]

Closed via #2749